In order to charge their customers properly, and generally for purposes of effective network administration, network service providers have a strong interest in accurately determining the presence of connectivity within their networks. This is true for many specific types of networks, including networks using Multi-Protocol Label Switching (MPLS). MPLS is a standard technique for routing packets over label switched paths (LSPs) in an internet protocol (IP) network, using labels that are attached to IP (Internet Protocol) packets. Traffic in MPLS networks is organized into forwarding equivalence classes (FECs). A given label switched path may carry traffic associated with one or more FECs. The routers forwarding packets within an MPLS network are referred to as label switched routers (LSRs).
A number of challenges exist in determining the presence of connectivity between LSRs in an MPLS network. For example, it would be desirable to monitor connectivity over a path between an ingress LSR and an egress LSR, with respect to the ingress LSR in combination with identification of the LSP at the ingress LSR. For purposes herein, the combination of an identifier of such an ingress LSR and a local identification of the LSP at that LSR is referred to as an ingress access point of the LSP. A system that addresses this need should be designed to accommodate the fact that an egress LSR for an LSP has no a priori knowledge of the set of relevant ingress access points for a given FEC. Additionally, over time, the set of ingress access points, or the egress LSR for a label switched path (LSP) may change. Further complications result from the fact that LSRs at the edge of a network may use multiple interfaces to forward traffic for a given FEC, in order to provide load balancing.
These and other conditions result in a need for a new system for measuring connectivity between LSRs in an MPLS network.